Transitioning out of sleep sack- what does your baby sleep in?

CB

I want to transition my 8 month old out of his sleep sack and into pjs, but I don’t know what he should wear for daytime naps. I feel like he would be cold in just a onesie, should I put pants on him? Socks? I don’t want to change him into pjs for every nap. What do people do?